I'm just an amateur, probably why I find the de Broglie/Bohm/Couder approach to QM compelling. But Copenhagen struck back: in a coincidence, Bohr's grandson is a fluid physicist who claims that Couder drops can't reproduce the quantum interference in a double slit experiment if you add a long wall that separates the paths from the source to the two slits. He says the drop will stay on one side of the wall, so the wave on the other side will dissipate. I can think of at least two problems:

  • Can't the drop tunnel through the wall? Bohm says the drop choosing one side breaks the symmetry necessary for interference, but since the drop may symmetrically choose either side and tunnel to the other, isn't symmetry preserved?
  • The ideal fluid is supposed to be non-dissipative, so couldn't something focus the wave such that it would regenerate indefinitely?
  • $\begingroup$ The superfluidity tag is for the non-dissipative fluid. I also wanted to tag fluid-dynamics but can only have 5 :( $\endgroup$ – user1441998 Dec 15 '18 at 3:59

The de Broglie/Bohm pilot wave theory was specifically designed to give exactly the same results in wave mechanics* as the Copenhagen interpretation. This was explained by Kofler and Zeilinger (arXiv link) as follows:

While the testable predictions of Bohmian mechanics are isomorphic to standard Copenhagen quantum mechanics, its underlying hidden variables have to be, in principle, unobservable.

Because there is simply no way to "see" the hidden variables in the pilot wave theory, it is possible for it to duplicate all the predictions of the Bohr/Born probabilistic interpretation.

This has a number of immediate consequences. One is that many people of a positivist inclination think that there is no actual meaningful difference between the two interpretations; the only distinctions are unobservable (and hence meaningless) metaphysics.

The second implication is that no real experiment is every going to be capable of proving or disproving the pilot wave explanation of the wave function. So no experiment that is performed with fluids has any bearing on whether the pilot wave theory is correct. The fluid experiments are kind of interesting as rough analogues of the quantum setup, but they are not (and cannot be) similar enough to resolve questions about whether the pilot wave theory is correct.

*For whatever it's worth, the de Broglie/Bohm theory does have a much more important and well known failure. While it provides an isomorphic description of propagating wave functions with a continuous state space, it is unable to describe discrete quantum systems, such as spin.

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  • $\begingroup$ well perhaps there are crucial unobservables even in classical systems. but here i'm asking if Bohr's argument works, since it seems to neglect tunneling and superfluidity. $\endgroup$ – user1441998 Dec 15 '18 at 4:35
  • $\begingroup$ @user1441998 Those details are irrelevant, and Bohr's contention has to be wrong, since the two theories give identical predictions in wave mechanics. $\endgroup$ – Buzz Dec 15 '18 at 4:58
  • $\begingroup$ well Bohr is criticizing Couder, not Bohm... that's what I'm asking about $\endgroup$ – user1441998 Dec 15 '18 at 5:01
  • $\begingroup$ @user1441998 That article contradicts itself as to whether the fluid results can refute the pilot wave theory. However, upon careful rereading, I think the confusion is the fault of the writer, and Bohr is not claiming that he can prove de Broglie and Bohm wrong. $\endgroup$ – Buzz Dec 15 '18 at 5:07
  • $\begingroup$ right, but he does claim Couder is wrong that the walking drop experiments can recapitulate double slit (with wall) interference. so my question is whether his argument stands despite tunneling, superfluidity, or other factors. $\endgroup$ – user1441998 Dec 15 '18 at 5:26

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